Processing facilities and other facilities routinely include tanks for storing liquid and other materials. For example, storage tanks are routinely used in tank farms and other storage facilities to store oil or other materials. As another example, oil tankers and other transport vessels routinely include numerous tanks storing oil or other materials. Processing facilities also include tanks for implementing an industrial process, such as receiving material through an input of the tank while allowing material to leave through an output of the tank (e.g., in oil refining operations or chemical production).
Often times it is necessary or desirable to measure the amount of material stored in a tank, for example, in order to control the level of material in the tank to be at a desired level during an industrial process of receiving or releasing material in the tank. Radar gauges can be used to measure an amount of material stored in a tank. Radar gauges transmit signals towards a material in a tank and receive signals reflected off the material in the tank.
Microwave level gauge or radar level gauge systems are in wide use for determining the fill level of a product contained in a tank. Radar level gauging is generally performed either by means of non-contact measurement, whereby electromagnetic signals are transmitted using a “free space” mode without a guide towards the product contained in the tank or by means of contact measurement, often referred to as guided wave radar (GWR), whereby electromagnetic signals are guided towards and into the product by a probe acting as a guided wave transmission line.
Such a probe is generally arranged to extend vertically from the top towards the bottom of the tank. The probe may also be arranged in a measurement tube, a so-called chamber, which is connected to the outer wall of the tank and is in fluid connection with the inside of the tank. Typically, the probe extends from a transmitter/receiver assembly into the product inside the tank, or chamber, via a sealing arrangement which may form a hermetic barrier. The most common type of guided wave radar uses short pulses (around 1 ns) without carrier and occupies a frequency range of roughly 0.1-1 GHz.
GWR is commonly used in the process industry to measure the product level in such tanks. GWR uses time domain reflectometry to measure the distance to the product. In GWR measurement systems, a waveguide is used to direct a short (e.g., ˜1 ns) EM pulse towards the surface of the medium in the tank. For deep tanks (e.g., >6 m), stainless steel wire rope can be employed as a waveguide.
GWR devices may be configured in the context of different and multiple probe types. For example, one of these types involves the use of a coaxial probe which had a rod central conductor and a tube outer conductor. However, the high temperature and pressure version of this type probe utilizes brittle ceramic spacers, which are easy to break while assembling the probe in the field as must be done due to long total lengths. Furthermore, such a probe is quite complicated to assemble, is quite expensive, and its length cannot be trimmed in the field. Solutions are thus needed to overcome these problems.